Heretofore, a centrifugal separation method has been employed for removing blood cells from blood to obtain plasma or serum required for clinical laboratory. However, with the centrifugal separation method, operation in a coagulating process or a process of transferring supernatant plasma or serum after separation was complicated. In addition, it took a long time to obtain the result of examination, and a large and expensive centrifugal separator was necessary.
In order to solve the problems described above, various methods of separation and separators which are able to remove blood cells from blood and obtain plasma or serum required for clinical laboratory without using the centrifugal separator are proposed.
For example, an instrument for separating serum or plasma which is able to separate and collect the serum or plasma component from collected blood simultaneously or immediately after collection of blood sample is disclosed in Patent Document 1 shown below. Referring to FIG. 11, the instrument for separating serum or plasma disclosed in Patent Document 1 is described below.
As shown in vertical cross-section in FIG. 11, an instrument 101 for separating serum or plasma includes an external tube 102, a blood collection tube 103, a connecting member 104, and a separated liquid collection tube 105.
The external tube 102 has a cylindrical shape, and has an opening at a lower end 102a thereof. The external tube 102 has a blood collection needle 105 extending outward and inward from the center of an upper end surface 102b. The blood collection tube 103 includes a cylindrical container 106 and closing members 107, 108 attached to an upper end 106a and a lower end 106b of the cylindrical container 106. The closing members 107, 108 are formed of material which can be pierced through by a needle. Arranged in the interior of the blood collection tube 103 are a blood cell separation fiber material layer 109 on the side of the closing member 107 and a blood cell agglutination material layer 110 on the side of the closing member 108. The interior of the blood collection tube 103 is decompressed. In FIG. 11, the blood collection tube 103 is inserted into the external tube 102 from the opening at the lower end 102a of the external tube 102.
The separated liquid collection tube 105 includes an opening 105a at one end. The opening 105a is provided with a closing member 111 which allow a needle to be pierced therethrough. The interior of the separated liquid collection tube 105 is decompressed. The connecting member 104 is formed into a cylindrical shape, and has a partitioning wall 104a at the center thereof. The connecting member 104 includes a hollow needle 112 extending upward and downward from the center of the partitioning wall 104a. 
When using the above-described instrument 101 for separating serum or plasma, the one end 105a of the blood collection needle 105 positioned outside the external tube 102 is inserted into a blood vessel. Simultaneously, the blood collection tube 103 is further inserted into the external tube 102, and the closing member 107 is pierced through by the other end 105b of the blood collection needle 105 opposite to the one end 105a. Consequently, blood flows into the interior of the blood collection tube 103 being decompressed. After a required amount of blood is flowed therein, the one end 105a of the blood collection needle 105 is pulled out from the blood vessel.
Subsequently, the closing member 108 of the blood collection tube 103 is pierced through by one end 112a of the hollow needle 112 of the connecting member 104. Simultaneously, the other end 112b of the hollow needle 111 of the connecting member 104 on the opposite side from the one end 112a pierces through the closing member 111 of the separated liquid collection tube 105. Consequently, blood flowed into the blood collection tube 103 is drawn into the separated liquid collection tube 105 by vacuum. At this time, the blood passes through the blood cell separation fiber material layer 109 and the blood cell agglutination material layer 110, and serum or plasma components are separated from blood. The separated serum or plasma components flow into the separated liquid collection tube 105 through the hollow needle 112.
Patent Document 1: JP-A-05-93721